Impedance shifting circuit and signal sensing circuit

ABSTRACT

A signal sensing circuit is provided. The signal sensing circuit comprises a first current-to-voltage circuit, a second current-to-voltage circuit and an impedance shifting circuit. The first current-to-voltage circuit converts a first input current into a first voltage that is directly proportional to a first impedance. The second current-to-voltage circuit converts a second input current into a second voltage that is directly proportional to a second impedance. The impedance shifting circuit generates a third voltage according to the first voltage, wherein the first impedance/the second impedance=K(first voltage/third voltage), where K is a real number.

CROSS REFERENCE TO RELATED PATENT APPLICATION

This patent application is a continuation application of U.S. patentapplication Ser. No. 13/792,960 filed on Mar. 11, 2013 which claims thedomestic priority of the U.S. provisional application 61/609,466 filedon Mar. 12, 2012, and hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a signal sensing circuit, and moreparticularly, to a signal sensing circuit across integrated circuits.

2. Description of the Prior Art

Referring to FIG. 1, a schematic diagram illustrating a detectingcircuit for a capacitive touch sensor is shown. When a driven electrodeT_(x1) provided with an AC driving signal, capacitive couplings will becreated between the driven electrode T_(x1) and sensed electrodes R_(x1)and R_(x2) overlapping with the driven electrode T_(x1). Signals of thesensed electrodes R_(x1) and R_(x2) can be converted into outputvoltages V′ and V″ by a front-end current sensing circuit, respectively.The output voltages V′ and V″ are related to the impedance of areference resistor R. Since background interferences affecting adjacentsensed electrodes will be similar, subtracting the signals of a pair ofadjacent sensed electrodes can effectively cancel out the common-modenoise and increase the signal-to-noise (S/N) ratio. Thus, the outputvoltages V′ and V″ can be converted into respective digital signalsthereof through an A/D converter and subtracted from each other, so asto create a digital signal representing the difference between theoutput voltages V′ and V″ by digital subtraction. The output voltages V′and V″ can be converted into a digital signal representing thedifference between the output voltages V′ and V″ using an A/D converteras a subtractor, in other words, by analog subtraction.

In order to effectively reduce the interferences, signals of all thesensed electrodes have to be received simultaneously in order tosimultaneously eliminate the interferences of the common-mode noise.Thus, the signal of each sensed electrode is coupled to a pin of anintegrated circuit (IC). Since the number of pins of the IC coupled withthe sensed electrodes is fixed, in the case of a large touch sensor, thenumber of the sensed electrodes may exceed the number of pins of asingle IC used for coupling with the sensed electrodes; as a result,several ICs have to be connected together in series.

Referring now to FIG. 2, when two ICs are connected in series, thesignals of a pair of adjacent sensed electrodes may be generated bydifferent ICs. Each IC will have its own manufacturing processvariations. Even if the same element adopts the same design, theelements manufactured using the same design may still have variationsamong them. For example, the same resistors are designed with the sameimpedance, but the actual impedances after manufacturing may bedifferent due to variations in the manufacturing process, which willinfluence the associated signals.

For example, an output voltage V′ generated based on an input current I′is associated with a reference resistor R′, and an output voltage V″generated based on an input current I″ is associated with a referenceresistor R″, wherein the reference resistors R′ and R″ are supposed tobe designed to have the same impedance. In the example of FIG. 1, theoutput voltages V′ and V″ are generated in the same IC, and thedifference between the output voltages V′ and V″ is Vd. Assumingmanufacturing process variations exist between the first integratedcircuit IC1 and the second integrated circuit IC2, the impedance of thereference resistor R1 is k (a constant value) times that of thereference resistor R″, thus the difference between the output voltagesV′ and V″ will not be Vd, creating an error. Such an error will varywith the degree of manufacturing process variations, which makes itdifficult to determine or correct.

From the above it is clear that prior art still has shortcomings. Inorder to solve these problems, efforts have long been made in vain,while ordinary products and methods offering no appropriate structuresand methods. Thus, there is a need in the industry for a novel techniquethat solves these problems.

SUMMARY OF THE INVENTION

Integrated circuits of the same design may have differences due tomanufacturing process variations. When calculations based on signals ofdifferent ICs are required, the manufacturing process variations mayresult in serious errors. The present invention thus provides a signalsensing circuit across integrated circuits, such that a signal of afirst IC inputting into a second IC may be automatically correctedaccording to the manufacturing process variations between the second ICand the first IC.

The above and other objectives of the present invention can be achievedby the following technical scheme. A signal sensing circuit proposed bythe present invention may include: a first current-to-voltage circuitfor converting a first input current into a first voltage that isdirectly proportional to a first impedance; a second current-to-voltagecircuit for converting a second input current into a second voltage thatis directly proportional to a second impedance; and an impedanceshifting circuit for generating a third voltage according to the firstvoltage, wherein the first impedance/the second impedance=K(firstvoltage/third voltage), where K is a real number. In an embodiment, Kequals 1.

The above and other objectives of the present invention can also beachieved by the following technical scheme. A signal sensing circuitproposed by the present invention may include: a first integratedcircuit including: a first input resistor for receiving a first voltage;a first inverting closed-loop amplifier including a first positiveinput, a first negative input and a first output, the first outputforming a first closed loop through a first reference resistor coupledto the first negative input, and the first negative input receiving afirst voltage input via the first input resistor, wherein the firstinput resistor and the first reference resistor are designed to have thesame impedance value; a second input resistor coupled to the firstoutput; and a first external pin coupled to the first output via thesecond input resistor; and a second integrated circuit including: asecond external pin electrically coupled to the first external pinoutside the second integrated circuit; and a second invertingclosed-loop amplifier including a second positive input, a secondnegative input and a second output, the second output forming a secondclosed loop through a second reference resistor coupled to the secondnegative input, and the second negative input coupled to the secondinput resistor via the second external pin, wherein the second inputresistor and the second reference resistor are designed to have the sameimpedance value.

The above and other objectives of the present invention can also beachieved by the following technical scheme. A signal sensing circuitproposed by the present invention may include: N input voltages arrangedin a row forming N−1 pairs of input voltages, wherein the i^(th) inputvoltage pair is formed by the N−i^(th) input voltage and the N−i+1^(th)input voltage, and N and i are a natural number greater than 1 and anatural number greater than 0 and less than N−1, respectively; a portionof an impedance shifting circuit including: a first input resistor forreceiving the N^(th) input voltage; a first inverting closed-loopamplifier including a first positive input, a first negative input and afirst output, the first output forming a first closed loop through afirst reference resistor coupled to the first negative input, and thefirst negative input coupled to the N^(th) input voltage via the firstinput resistor, wherein the first input resistor and the first referenceresistor are designed to have the same impedance value; a second inputresistor coupled to the first output; and a second portion of theimpedance shifting circuit including: a second inverting closed-loopamplifier including a second positive input, a second negative input anda second output, the second output forming a second closed loop througha second reference resistor coupled to the second negative input, andthe second output and the N^(th) input voltage forming the N^(th) inputvoltage pair, wherein the second input resistor and the second referenceresistor are designed to have the same impedance value.

With the above technical schemes, the present invention achieves atleast the following advantage and beneficial effect: a signal of a firstintegrated circuit inputting into a second integrated circuit isautomatically corrected according to the manufacturing processvariations between the second integrated circuit and the firstintegrated circuit.

The above description is only an outline of the technical schemes of thepresent invention. Preferred embodiments of the present invention areprovided below in conjunction with the attached drawings to enable onewith ordinary skill in the art to better understand said and otherobjectives, features and advantages of the present invention and to makethe present invention accordingly.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more fully understood by reading thefollowing detailed description of the preferred embodiments, withreference made to the accompanying drawings, wherein:

FIG. 1 is a schematic diagram illustrating a detecting circuit for acapacitive touch sensor;

FIG. 2 is a schematic diagram illustrating connections between twodetecting circuits for capacitive touch sensors;

FIG. 3 is a schematic diagram illustrating a signal sensing circuitacross integrated circuits in accordance with the present invention; and

FIG. 4 is a schematic diagram illustrating a signal sensing circuitinside an integrated circuit in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Some embodiments of the present invention are described in detailsbelow. However, in addition to the descriptions given below, the presentinvention can be applicable to other embodiments, and the scope of thepresent invention is not limited by such, rather by the scope of theclaims. Moreover, for better understanding and clarity of thedescription, some components in the drawings may not necessary be drawnto scale, in which some may be exaggerated relative to others, andirrelevant parts are omitted.

The present invention provides a signal sensing circuit, which mayinclude: a first current-to-voltage circuit, a second current-to-voltagecircuit and an impedance shifting circuit. The first current-to-voltagecircuit converts a first input current into a first voltage that isdirectly proportional to a first impedance. The secondcurrent-to-voltage circuit converts a second input current into a secondvoltage that is directly proportional to a second impedance, wherein thefirst current-to-voltage circuit and the second current-to-voltagecircuit reside on separate integrated circuits, and the first impedanceand the second impedance are designed to have the same impedance value.In addition, the impedance shifting circuit generates a third voltageaccording to the first voltage, wherein the first impedance/the secondimpedance=K(the first voltage/the third voltage), where K is a realnumber. In an embodiment, K equals 1., i.e. the first impedance/thesecond impedance=the first voltage/the third voltage. Moreover, a firstportion of the impedance shifting circuit and the firstcurrent-to-voltage circuit reside on the same integrated circuit, and asecond portion of the impedance shifting circuit and the secondcurrent-to-voltage circuit reside on the same integrated circuit.

Referring to FIG. 3, a schematic diagram illustrating a signal sensingcircuit proposed by the present invention. The first portion of theimpedance shifting circuit described before may include a first inputresistor R1, a first inverting closed-loop amplifier and a second inputresistor R2. The first input resistor R1 receives a first voltage V. Thefirst inverting closed-loop amplifier includes a first positive input, afirst negative input and a first output. The first output forms a firstclosed loop through a first reference resistor R1′ coupled to the firstnegative input, and the first negative input receives the first voltageinput V via the first input resistor R1, wherein the first inputresistor R1 and the first reference resistor R1′ are designed to havethe same impedance value. In addition, the second input resistor R2 iscoupled to the first output, which receives a voltage of the firstoutput.

The second portion of the impedance shifting circuit described beforemay be a second inverting closed-loop amplifier, which includes a secondpositive input, a second negative input and a second output. The secondoutput forms a second closed loop through a second reference resistorR2′ coupled to the second negative input, and the second negative inputis coupled with the second input resistor R2 via a second external pin,wherein the second input resistor and the second reference resistor aredesigned to have the same impedance value. In addition, the secondoutput generates a third voltage V3.

In an example of the present invention, the first and second portions ofthe impedance shifting circuit reside on a first integrated circuit IC1and a second integrated circuit IC2, respectively, and are coupled toeach other through a first external pin P1 of the first integratedcircuit IC1 and a second external pin P2 of the second integratedcircuit IC2. The first external pin P1 and the second external pin P2can be pins outside the packaged integrated circuits and used asinterfaces for coupling the inside of the ICs to the outside.

The impedance shifting circuit mentioned above is merely an example ofthe present invention, and the present invention is not limited to this.The impedance shifting circuit generates the third voltage V3 based onthe first voltage V. Since the second input resistor R2 of the firstportion of the impedance shifting circuit on the first integratedcircuit is designed to have the same impedance value as the secondreference resistor R2′ of the second portion of the impedance shiftingcircuit on the second integrated circuit, if the actual impedance valuesof the second input resistor R2 and the second reference resistor R2′are the same, the first voltage V will be equal to the third voltage V3.

In addition, the above first current-to-voltage circuit can be a thirdinverting closed-loop amplifier, which includes a third positive input,a third negative input and a third output. The third output forms athird closed loop through a third reference resistor R3′ coupled to thethird negative input, and the third negative input receives a firstinput current I1. Moreover, the above second current-to-voltage circuitcan be a fourth inverting closed-loop amplifier, which includes a fourthpositive input, a fourth negative input and a fourth output. The fourthoutput forms a fourth closed loop through a fourth reference resistorR4′ coupled to the fourth negative input, and the fourth negative inputreceives a second input current I1. Furthermore, the third referenceresistor R3′ and the fourth reference resistor R4′ are designed to havethe same impedance value.

The first current-to-voltage circuit and the second current-to-voltagecircuit mentioned above are merely examples of the present invention,and the present invention is not limited to these. One with ordinaryskill in the art can appreciate the implementations of othercurrent-to-voltage circuits, and they will not be described in detailsherein. In other words, a current-to-voltage circuit applicable to thepresent invention can be any equivalent circuit that converts an inputcurrent into an output voltage which is directly proportional to areference impedance of the current-to-voltage circuit.

Thus, the ratio between the (actual) impedance of the third referenceresistor R3′ and the (actual) impedance of the fourth reference resistorR4′=the ratio between the (actual) impedance of the second inputresistor R2 and the (actual) impedance of the second reference resistorR2′=the voltage of the third output/the voltage of the second output. Inother words, the error in the first voltage due to manufacturing processvariations will be corrected by the current-to-voltage circuits.

The present invention may further include a subtractor for generating adifference between the signal of the second output and the signal of thefourth output, that is, a difference between the third voltage and thesecond voltage. In an example of the present invention, the subtractorcan be implemented with an A/D converter, and the difference between thesignal of the second output and the signal of the fourth output is adigital signal.

In an example of the present invention, the first integrated circuit IC1and the second integrated circuit IC2 have the same design. Referringnow to FIG. 4, a schematic diagram illustrating another signal sensingcircuit in accordance with another example of the present invention isshown. The signal sensing circuit may include N first current-to-voltagecircuits as described above, each for converting a first input currentto a first voltage that is directly proportional to a first impedance;and a first portion and a second portion of an impedance shiftingcircuit.

In this example, an example of the first current-to-voltage circuits canbe the aforementioned third inverting closed-loop amplifier. Each thirdinverting closed-loop amplifier, which includes a third positive input,a third negative input and a third output. The third output forms athird closed loop through a third reference resistor R3 coupled to thethird negative input, wherein each third negative input receives aninput current I, and each third inverting closed-loop amplifier providesa first voltage V based on the received input current I. In addition,each third reference resistor R3 may be designed to have the sameimpedance.

The first portion of the impedance shifting circuit may include a firstinput resistor R1, a first inverting closed-loop amplifier and a secondinput resistor R2. The first input resistor R1 receives the firstvoltage V. The first inverting closed-loop amplifier includes a firstpositive input, a first negative input and a first output. The firstoutput forms a first closed loop through a first reference resistor R1′coupled to the first negative input, and the first negative input iscoupled to the N^(th) first voltage input V via the first input resistorR1, wherein the first input resistor R1 and the first reference resistorR1′ are designed to have the same impedance value. In addition, thesecond input resistor R2 is coupled to the first output, which receivesa voltage of the first output.

The second portion of the impedance shifting circuit may be a secondinverting closed-loop amplifier, which includes a second positive input,a second negative input and a second output. The second output forms asecond closed loop through a second reference resistor R2′ coupled tothe second negative input, and the second output and the first firstvoltage V form an N^(th) pair of input voltages, wherein the secondinput resistor R2 and the second reference resistor R2′ are designed tohave the same impedance value. In addition, the second output generatesa third voltage V3.

The present invention may further include N subtractors arranged in arow. Each subtractor calculates a difference between a pair of inputvoltages, wherein the j^(th) subtractor calculates a difference betweena j^(th) pair of input voltages, wherein j is a natural number greaterthan 0 and less than N. Each subtractor can be an A/D converter and thecalculated difference is a digital signal. One with ordinary skill inthe art can appreciate that the subtractors can be implemented bydifferential amplifiers or other types of subtractor circuits.

The signal sensing circuit shown in FIG. 4 can be integrated into anintegrated circuit. When two integrated circuits of the same design areconnected in series, a first external pin P1 of the first integratedcircuit is coupled to a second external pin P2 of the second integratedcircuit.

The above embodiments are only used to illustrate the principles of thepresent invention, and they should not be construed as to limit thepresent invention in any way. The above embodiments can be modified bythose with ordinary skill in the art without departing from the scope ofthe present invention as defined in the following appended claims.

What is claimed is:
 1. An impedance sifting circuit, comprising: a firstintegrated circuit, including: a first input resistor for receiving afirst voltage; a first inverting closed-loop amplifier, including afirst positive input, a first negative input and a first output, whereinthe first output forming a first closed loop through a first referenceresistor coupled to the first negative input and the first negativeinput receiving a first voltage input via the first input resistor,wherein the first input resistor and the first reference resistor aredesigned to have the same impedance; a second input resistor coupled tothe first output; and a first external pin coupled to the first outputvia the second input resistor; and a second integrated circuit,including: a second external pin electrically coupled to the firstexternal pin outside the second integrated circuit; and a secondinverting closed-loop amplifier, including a second positive input, asecond negative input and a second output, wherein the second outputforming a second closed loop through a second reference resistor coupledto the second negative input, and the second negative input coupled tothe second input resistor via the second external pin, wherein thesecond input resistor and the second reference resistor are designed tohave the same impedance.
 2. A first impedance shifting circuit inside afirst integrated circuit, comprising: a first input resistor forreceiving a first voltage; a first inverting closed-loop amplifier,including a first positive input, a first negative input and a firstoutput, wherein the first output forming a first closed loop through afirst reference resistor coupled to the first negative input and thefirst negative input receiving a first voltage input via the first inputresistor, wherein the first input resistor and the first referenceresistor are designed to have the same impedance; and a second inputresistor coupled to the first output, wherein the first output coupledto the second input resistor connects to a second impedance shiftingcircuit of a second integrated via an external pin.
 3. The firstimpedance shifting circuit of claim 2, wherein the second impedanceshifting circuit comprises a second inverting closed-loop amplifier,wherein the second inverting closed-loop amplifier including a secondpositive input, a second negative input and a second output, wherein thesecond output forming a second closed loop through a second referenceresistor coupled to the second negative input, and the second negativeinput coupled to the second input resistor via the second external pin,wherein the second input resistor and the second reference resistor aredesigned to have the same impedance.
 4. A signal sensing circuit of acapacitive touch sensor, including a first sensing electrode and asecond sensing electrode, wherein the signal sensing circuit comprising:a first current-to-voltage circuit inside a first integrated circuit,configured for connecting to the first sensing circuit and converting afirst input current from the first sensing circuit into a first voltage,wherein the first voltage is proportional to a first impedance; a secondcurrent-to-voltage circuit inside a second integrated circuit,configured for connecting to the second sensing circuit and converting asecond input current from the second sensing circuit into a secondvoltage, wherein the second voltage is proportional to a secondimpedance; and an impedance shifting circuit for generating a thirdvoltage according to the first voltage, wherein a ratio of the firstimpedance and the second impedance equals to a ratio of the firstvoltage and the third voltage, wherein the first impedance and thesecond impedance are designed to be equaled, wherein a first part of theimpedance shifting circuit is located in the first integrated circuit, asecond part of the impedance shifting circuit is located in the secondintegrated circuit.
 5. A signal sensing circuit of a capacitive touchsensor, including a first sensing electrode and a second sensingelectrode, wherein the signal sensing circuit comprising: a firstintegrated circuit, including: a first current-to-voltage circuit forconnecting to the first sensing circuit and converting a first inputcurrent from the first sensing circuit into a first voltage; a firstinput resistor for receiving a first voltage; a first invertingclosed-loop amplifier, including a first positive input, a firstnegative input and a first output, wherein the first output forming afirst closed loop through a first reference resistor coupled to thefirst negative input and the first negative input receiving a firstvoltage input via the first input resistor, wherein the first inputresistor and the first reference resistor are designed to have the sameimpedance; a second input resistor coupled to the first output; a firstexternal pin coupled to the first output via the second input resistor;and a third inverting closed-loop amplifier, including a third positiveinput, a third negative input and a third output, wherein the thirdoutput forming a third closed loop through a third reference resistorcoupled to the third negative input and the third negative inputreceiving the first input current; and a second integrated circuit,including: a second current-to-voltage circuit for connecting to thesecond sensing circuit and converting a second input current from thesecond sensing circuit into a second voltage; a second external pinelectrically coupled to the first external pin outside the secondintegrated circuit; a second inverting closed-loop amplifier, includinga second positive input, a second negative input and a second output,wherein the second output forming a second closed loop through a secondreference resistor coupled to the second negative input, and the secondnegative input coupled to the second input resistor via the secondexternal pin, wherein the second input resistor and the second referenceresistor are designed to have the same impedance; and a fourth invertingclosed-loop amplifier, including a fourth positive input, a fourthnegative input and a fourth output, wherein the fourth output forming afourth closed loop through a fourth reference resistor coupled to thefourth negative input and the fourth negative input receiving the secondinput current, wherein the third reference resistor and the fourthreference resistor are designed to have the same impedance.
 6. Thesignal sensing circuit of claim 5, wherein a ratio of impedance of thethird reference resistor and impedance of the fourth reference resistorequals to a ratio of voltage of the third output and voltage of thesecond output.
 7. The signal sensing circuit of claim 5, furthercomprises a subtractor for generating a difference between a signal ofthe second output and a signal of the fourth output.
 8. The signalsensing circuit of claim 7, wherein the subtractor is ananalog-to-digital converter, and the difference between the signal ofthe second output and the signal of the fourth output is a digitalsignal.